Mold components used in injection molding of thermoplastic resins, and injection molding method for thermoplastic resins.

Abstract

To provide mold parts that do not generate periodic irregularities (scale patterns) that appear in a direction perpendicular to a drawing direction (MD) of the mold parts having a surface to contact and slide on a molded product in parallel therewith when the molded product is taken out from a mold after injection molding of thermoplastic resins (particularly heat-meltable fluororesins), an injection molding method that uses them, and the molded product that does not have periodic irregularities (scale patterns) that appear in the direction perpendicular to the drawing direction (MD) of the mold parts.SOLUTION: Mold parts used for injection molding of thermoplastic resin includes a surface to contact and slide on a molded product in substantially parallel therewith when the molded product is taken out from a mold after injection molding. An average tilt angle in a sliding direction (MD) is 1.5° or more. There are also provided an injection molding method that uses the mold parts, and molded products.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a mold part (especially a core pin) suitable for injection molding of a thermoplastic resin (especially a heat-melting fluororesin), an injection molding method, and a molded product.

Background Art

[0002] Since fluororesins are excellent in chemical resistance, they are used for chemical solution tubes and tube joints used in semiconductor manufacturing equipment. Injection molding methods are used for those with complex shapes such as tube joints. On the other hand, in semiconductor manufacturing, if minute foreign substances (referred to as particles) adhere to the silicon substrate, it will lead to the occurrence of defective products. Therefore, the inner surface of the tube joint for chemical solutions used in semiconductor manufacturing equipment needs to be as clean as possible. For this reason, a smooth surface without any unevenness that may cause foreign substances (particles) to stay or become a source of foreign substances (particles) is required.

[0003] However, those having a hollow structure such as a joint are molded by pulling out the core part of the mold that forms the hollow after resin injection. It has been found that periodic unevenness (scale pattern) occurs in the direction perpendicular to the pulling direction (MD) of the core part (core pin) of the mold. This periodic unevenness (scale pattern) is presumed to be due to the interaction between the surface of the mold part (especially the core pin) and the resin, and there is a possibility of solution by improving the mold release property. However, generally, in injection molding, a mold release agent is applied to the mold to improve the mold release property of the molded body. However, since the mold release agent itself can be a factor of impurities, using a mold release agent is not suitable for molding of objects that require cleanliness.

[0004] In particular, in the molding of chemical tubes and tube fittings for semiconductor manufacturing equipment using fluororesins, fluororesins (especially PFA) have a high melting point, and molding is done at high temperatures. This raises concerns that release agents may volatilize, causing defects or impurities (particles), making their use impossible. Therefore, there is a need for mold components, injection molding methods (and molded products) that do not produce periodic irregularities (scale patterns) that appear perpendicular to the withdrawal direction (MD) of the mold component.

[0005] Patent Document 1, described below, describes a method for manufacturing a resin container that is highly transparent and less susceptible to the adsorption of proteins and the like onto its inner wall, which involves using a mold core with a surface roughness (Ra) of 0.02 to 0.20 μm. However, even when using mold components with such extremely smooth surfaces, periodic irregularities (scale-like patterns) appear in a direction perpendicular to the drawing direction (MD) (Comparative Examples 1 to 3 of this application).

[0006] On the other hand, Patent Document 2 below describes a mold release method in injection molding, in which, when a molded product is released from the mold by opening the mold after an insert member for forming a through hole or recess in the cavity of the molding die has been placed inside the mold cavity, the insert member is pulled out from the molded product and then reinserted into its original position to release the molded product from the mold. However, this method has the disadvantage of reducing productivity. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-155327 [Patent Document 2] Special Publication No. 6-94148 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a mold component that does not produce periodic irregularities (scale-like patterns) that appear perpendicular to the withdrawal direction (MD) of the mold component having a surface that slides parallel to the molded product when the molded product is removed from the mold after injection molding of a thermoplastic resin (particularly a heat-meltable fluororesin), an injection molding method using the same, and a molded product that does not exhibit periodic irregularities (scale-like patterns) that appear perpendicular to the withdrawal direction (MD) of the mold component. [Means for solving the problem]

[0009] This invention has found that by using a mold component that has a surface that slides substantially parallel to the molded product when the molded product is removed from the mold after injection molding, and that has a specific surface condition, it is possible to suppress the occurrence of periodic irregularities (scale-like patterns) on the surface of the molded product that appear perpendicular to the withdrawal direction (MD) of the mold component.

[0010] In other words, the present invention is as follows: 1. A mold component used in injection molding of thermoplastic resins, having a surface that slides substantially parallel to the molded product when removing the molded product from the mold after injection molding, The surfaces that are in contact with each other Sliding direction (MD) The angle at which a straight line obtained by connecting two consecutive observation points intersects with a straight line parallel to the sliding surface was averaged over the observation range. Mold parts with an average inclination angle of 1.5° or more. 2. A mold component as described in 1, which is a core pin for forming the hollow portion of a molded product. A method for injection molding thermoplastic resin using mold components described in 3.1-2. 4. The injection molding method according to 3, wherein the thermoplastic resin is a heat-meltable fluororesin. 5. The injection molding method according to 3 to 4, characterized in that the extraction speed for removing the molded part after injecting resin into the mold and molding is 20 mm / sec or less. 6. A molded article of thermoplastic resin formed by injection molding using a mold component having a surface that slides parallel to the molded article when removing the molded article, wherein the average inclination angle of the mold withdrawal direction (MD) of the molded article surface is 1.5° or less. 7. A molded part of item 6, which is a fitting component for chemical solutions. [Effects of the Invention]

[0011] According to the present invention, there are provided a mold part, an injection molding method, and a molded product having no periodic unevenness (scale pattern) in a direction perpendicular to the drawing direction (MD) of the mold part on the surface of the molded product without using a mold release agent.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is an explanatory view showing a hollow part of a molded product. [Figure 2] FIG. 2 is an explanatory view of an average inclination angle. [Figure 3] FIG. 3 is a cross-sectional view of a three-way joint for prototype evaluation. [Figure 4] FIG. 4 is a perspective view of a three-way joint for prototype evaluation. [Figure 5] FIG. 5 is a photograph of the three-way joint for prototype evaluation after being taken out of the mold. [Figure 6] FIG. 6 is a cross-sectional view of a core pin for prototype evaluation. [Figure 7] Photograph of the surface (inner surface of the joint) of the molded product obtained by injection molding at a draw speed of 4.5 mm / sec of the mold part (core pin) of Example 1. [Figure 8] Photograph of the surface (inner surface of the joint) of the molded product obtained by injection molding at a draw speed of 4.5 mm / sec of the mold part (core pin) of Comparative Example 2.

Modes for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. Injection molding is a molding method in which a resin melted by heating is poured into a mold, and after the resin cools and solidifies below the melting point, the resin is taken out of the mold to obtain a molded body.

[0014] The thermoplastic resin used in the injection molding of the present invention is a resin that exhibits melt fluidity when the temperature is above the melting point. For example, polyethylene, polypropylene, polybutylene terephthalate, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, polycarbonate, polyphthalamide, polyoxymethylene, polymethyl methacrylate, polyether ether ketone, polyamideimide, polyetherimide, polyphenylene sulfide, thermally fusible fluororesin, etc. can be used.

[0015] In the injection molding using the mold parts of the present invention, the above various thermoplastic resins can be used. However, since a molded product with a smooth surface can be obtained without using a mold release agent, it is particularly useful for molding chemical liquid pipes and joints used in semiconductor manufacturing using a thermally fusible fluororesin. A thermally fusible fluororesin is a fluororesin that exhibits melt fluidity when the temperature is above the melting point. For example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer, etc. can be used.

[0016] Among thermally fusible fluororesins, thermally fusible perfluoro resins such as low molecular weight PTFE, PFA, FEP, and tetrafluoroethylene-hexafluoropropylene-perfluoro(alkyl vinyl ether) copolymer are preferably used in applications such as chemical liquid pipes and joints because of their excellent chemical resistance. Among them, PFA has excellent heat resistance and is the most preferred. The perfluoro(alkyl vinyl ether) (PAVE) comonomer contained in PFA is preferably one in which the alkyl group has 1 to 5 carbon atoms, with perfluoroethyl vinyl ether (PEVE) having 2 carbon atoms and perfluoropropyl vinyl ether (PPVE) having 3 carbon atoms being preferred. When using PFA, it is preferable to use a PFA with high fluidity during melting in order to ensure defect-free resin filling of the mold during injection molding, and it is preferable to use a PFA with a melt flow rate (MFR) of 10 g / 10 min or more. Furthermore, the PFA molecular chain has a -CF3 group at the end, and the other unstable end groups have 10 carbon atoms. 6 It is preferable to use molds with 10 or fewer pieces per mold, as this is thought to improve mold release properties. It is possible to form -CF3 groups at the ends of polymer chains by treatment with fluorine gas, and this can be done by methods described in Japanese Patent Publication No. 62-104822, etc.

[0017] The mold component used in injection molding according to the present invention is a mold component having a surface that slides substantially parallel to the surface when removing the molded product after injection molding. Examples include a mold component (core pin) for forming a hollow portion and an injection molding die having a constituent surface substantially parallel to the direction of mold withdrawal after resin filling. In this invention, the surfaces that slide in substantially parallel to each other are surfaces that are within 5° of the direction in which the molded product is removed from the mold, or the direction in which the mold is withdrawn from the mold, when the molded product is removed from the mold.

[0018] The hollow section is a structure formed using one or more core pins, and its shape is not limited as long as the core pins can be removed after the resin has solidified. The hollow section may penetrate the molded body as shown in Figure 1A, or it may not penetrate as shown in Figure 1B. The hollow section may also be circular, square, or have other shapes as shown in Figure 1C. The hollow section may be curved as shown in Figure 1D, or it may intersect with other hollow sections as shown in Figure 1E.

[0019] The average inclination angle in the sliding direction (MD, withdrawal direction) of the mold components used in injection molding of the present invention is 1.5° or more. It is more preferable if it is 2.0° or more. There is no upper limit, but it is preferably 5.0° or less, more preferably 4.5° or less, and even more preferably 4.0° or less. The average tilt angle is a value obtained by analyzing the cross-sectional profile of a molded body using a measuring instrument such as a white light interference microscope. In this invention, the cross-sectional profile is a profile obtained by taking the position of the molded body surface in the sliding direction between the molded body and the die as the horizontal axis and the height of the molded body surface as the vertical axis. As shown in Figure 2, the average tilt angle is the average of the angles at which the straight line obtained by connecting two consecutive observation points that form the cross-sectional profile intersects with a straight line parallel to the sliding surface, within the observation range. In measuring the average tilt angle in this invention, an instrument with a resolution of 5 nm or more in the height direction (vertical axis) and a resolution of 1 μm or more in the width direction (horizontal axis) is required. As measurement conditions, the measurement length is 100 μm, the sampling interval is 0.54 μm, and the distance between cross-sectional profiles is 50 μm in the direction perpendicular to the sliding direction. The average of 10 measurements is used as the average tilt angle in this invention.

[0020] A small average tilt angle makes it easier for periodic irregularities (scale-like patterns) to occur that are perpendicular to the mold part's drawing direction (MD). On the other hand, if the average inclination angle is too large, large irregularities are transferred to the molded product, making it difficult to obtain a smooth surface.

[0021] In the injection molding method of the present invention, it is preferable that the extraction speed for pulling out the mold component to remove the molded product after the resin has been injected into the mold and molded is 20 mm / sec or less. More preferably, it is 10 mm / sec or less, even more preferably 5 mm / sec or less, and most preferably 3 mm / sec or less. This is because a high (fast) pull-out speed makes it easier for periodic irregularities (scale-like patterns) to appear perpendicular to the pull-out direction (MD) of the mold component. When a mold component is pulled out, the resin surface is subjected to shear stress, and a high pull-out speed increases the shear stress, causing a large deformation of the resin, which in turn makes it easier for periodic irregularities (scale-like patterns) to occur.

[0022] The material for the mold components used in the injection molding of the present invention can be any metal commonly used for injection molding molds of resins, such as stainless steel, pre-hardened steel, carbon steel, high-speed steel, nickel-chromium steel, and nickel-chromium-molybdenum steel. Among these, nickel-chromium-molybdenum steel is preferred. This is because fluororesins generate corrosive gases in their molten state, and molds are often plated with chromium or nickel to prevent corrosion. However, repeated molding can cause the plating to peel off, allowing corroded metal to enter the molded product and cause defects. Nickel-chromium-molybdenum steel, on the other hand, has high corrosion resistance and does not require plating, thus avoiding the above problem.

[0023] The molded product of the present invention has a smooth surface without periodic irregularities (scale-like patterns) that appear perpendicular to the withdrawal direction (MD) of the mold components. The presence or absence of periodic irregularities (scale-like patterns) can be confirmed by surface observation using a microscope, but it can also be evaluated by measuring the average inclination angle of the withdrawal direction (MD) of the mold components. If there are periodic irregularities (scale-like patterns), the average inclination angle increases, and the average inclination angle of the molded product surface in the die-draw direction (MD) is 1.5° or less. A value of 1.0° or less is preferable as it indicates a smoother surface. Even more preferable is a value of 0.5° or less.

[0024] Furthermore, there is no need to use a mold release agent, which has the advantage that no foreign matter derived from the mold release agent remains on the surface. As a result, the molded product of the present invention is suitable as a fitting component for chemical solutions in semiconductor manufacturing equipment made of heat-meltable fluororesin (especially PFA). [Examples]

[0025] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0026] (injection molding) Using a NEX180-36E injection molding machine manufactured by Nissei Plastic Industrial Co., Ltd., PFA (Teflon® PFA 440HP-J manufactured by Mitsui Chemours Fluoroproducts Co., Ltd. [tetrafluoroethylene / perfluoroethyl vinyl ether copolymer, MFR 15g / 10min, melting point 308℃, unstable end groups (-CH2OH end group, -CONH2 end group, -COF end group) with 10 carbon atoms] was used. 6 [Less than 6 pieces per unit] was injected and held for 30 seconds at a resin temperature of 380°C and a mold temperature of 160°C, with an injection pressure and holding pressure of 50 MPa and an injection speed of 6 mm / sec. After cooling for 10 seconds, the mold was opened, and the molded body was removed from the mold after 30 seconds to form the three-way joint shown in Figures 3 to 5. Three core pins were used to form the hollow section, and the mechanism was designed so that the core pins would be removed simultaneously with the opening of the mold. The core pin removal speeds were set to three levels: 15 mm / sec, 4.5 mm / sec, and 1.5 mm / sec. Regarding the shape of the core pin, the base of the part in contact with the resin is circular with a diameter of approximately 9.8 mm, the length of the insertion part is 50.47 to 60.77 mm (slightly different depending on the direction of each joint of the three-way joint (horizontal left / right direction, downward direction)), it tapers from the base to the tip with a slope of approximately 1.1° (1.0 to 1.2°), and the diameter of the tip is approximately 8.8 mm. Figure 6 shows the dimensions of the cross-section of the core pin that is inserted in the horizontal direction. There are six levels of core pins, but the external dimensions are the same for all of them. The material used is high-speed steel SKH51 (compliant with JIS G4403) with a chrome-plated surface or nickel-chromium-molybdenum steel (MA276 manufactured by Hitachi Metals, Ltd.).

[0027] (PFA melt flow rate) A melt indexer (manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a corrosion-resistant cylinder, orifice, and piston compliant with ASTM D1238-95 was used. 5g of the sample was filled into a cylinder maintained at 372±1℃ and held for 5 minutes. Then, under a 5kg load (piston and weight), the sample was extruded through the orifice, and the amount of molten material extruded per 10 minutes (g / 10 min) was determined as the MFR (Metal Flow Rate).

[0028] (Unstable terminal group of PFA) It is measured by the methods described in U.S. Patent No. 3,085,083 and U.S. Patent No. 4,675,380.

[0029] (Surface condition measurement) The method for measuring the surface condition (average inclination angle, surface roughness Ra) of mold parts and molded products according to the present invention is shown below. Using a scanning white-light interference microscope manufactured by Hitachi High-Tech Science Corporation, the sample surface was scanned with a 10x interference objective lens and the measurement mode set to wave. From the scanned three-dimensional image, 10 cross-sectional profiles in the sliding direction (MD) were acquired at 50 μm intervals in the direction perpendicular to the sliding direction (MD) (N=10). The arithmetic mean roughness (Ra) [μm] and mean tilt angle [°] of each obtained cross-sectional profile were averaged and used as the measured value. Furthermore, the presence or absence of periodic irregularities (scale-like patterns) was visually determined from microscopic image observation.

[0030] (Example 1) A surface-polished core pin made of MA276 material was subjected to blast treatment. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.202 μm, and the average tilt angle was 2.546°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1.

[0031] (Example 2) A surface-polished core pin made of MA276 material was subjected to blast treatment. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.263 μm, and the average tilt angle was 4.043°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1.

[0032] (Example 3) A core pin made of high-speed steel SKH51, which was chromium-plated and then surface-polished, was used. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.123 μm, and the mean tilt angle was 1.737°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1.

[0033] (Comparative Example 1) Core pins made of high-speed steel SKH51 were chromium-plated and then surface-polished, followed by a mirror finish treatment using fine blasting. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.048 μm, and the average tilt angle was 1.089°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1.

[0034] (Comparative Example 2) A core pin made of high-speed steel SKH51, which had been chromium-plated and then surface-polished, was used. The surface polishing was performed more finely than in Example 3 to achieve a smoother surface. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.059 μm, and the average tilt angle was 0.762°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1.

[0035] (Comparative Example 3) Core pins made of high-speed steel SKH51 were chromium-plated and then surface-polished, and then subjected to mirror-finish blasting. A finer blasting process was used than in Comparative Example 1. The arithmetic mean roughness (Ra) in the sliding direction (MD) was 0.030 μm, and the average tilt angle was 0.131°. Surface measurements were performed on the core pin sliding surface (inner surface of the joint) of the molded product (three-way joint) obtained by injection molding using this core pin in the manner described above. The results are shown in Table 1. At a core pin extraction speed of 15 mm / sec, the molded product tore apart when removed from the mold, resulting in no usable molded product.

[0036] (Table 1) JPEG0007865706000001.jpg77169

[0037] As an example of determining the presence or absence of periodic irregularities (scale-like patterns) using microscopic images (photographs), Figures 7 and 8 show images of the surface of a molded product (inner surface of a joint) obtained by injection molding at a mold component (core pin) withdrawal speed of 4.5 mm / sec in Example 1, and images of the surface of a molded product (inner surface of a joint) obtained by injection molding at a mold component (core pin) withdrawal speed of 4.5 mm / sec in Comparative Example 2, respectively. Figure 8 shows periodic irregularities (scale-like patterns), whereas Figure 7 shows some areas that resemble irregularities, but lacks the periodic irregularities (scale-like patterns). [Industrial applicability]

[0038] The present invention provides a mold component that, in injection molding of thermoplastic resins, does not produce periodic irregularities (scale-like patterns) that appear perpendicular to the withdrawal direction (MD) of the mold component having a surface that slides parallel to the molded product when the molded product is removed from the mold after injection molding; an injection molding method using the same; and a molded product that does not exhibit periodic irregularities (scale-like patterns) that appear perpendicular to the withdrawal direction (MD) of the mold component. In particular, since a molded product with a smooth surface can be obtained without using a release agent, it is especially useful for molding chemical pipes and fittings used in semiconductor manufacturing using heat-meltable fluororesins.

Claims

1. A mold component used in injection molding of thermoplastic resins, having a surface that slides substantially parallel to the molded product when the molded product is removed from the mold after injection molding, wherein the average inclination angle is the average of the angle at which a straight line obtained by connecting two consecutive observation points in the sliding direction (MD) of the sliding surface intersects with a straight line parallel to the sliding surface, measured using a device with a resolution of 5 nm or more in the height direction (vertical axis) and a resolution of 1 μm or more in the width direction (horizontal axis), under measurement conditions of a measurement length of 100 μm, a sampling interval of 0.54 μm, and a distance of 50 μm between cross-sectional profiles perpendicular to the sliding direction, and the average inclination angle is 1.5° or more.

2. A mold component according to claim 1, which is a core pin for forming a hollow portion of a molded product.

3. A method for injection molding a thermoplastic resin using the mold component described in claim 1 or 2.

4. The injection molding method according to claim 3, wherein the thermoplastic resin is a heat-meltable fluororesin.

5. The injection molding method according to claim 3 or 4, characterized in that the extraction speed for removing the molded part after injecting resin into the mold and molding is 20 mm / sec or less.

6. A molded article of thermoplastic resin molded by the injection molding method described in Claim 3, wherein the average inclination angle is the average of the angles at which a straight line obtained by connecting two consecutive observation points on the surface of the mold in the mold withdrawal direction (MD) intersects with a straight line parallel to the sliding surface, measured using a device with a resolution of 5 nm or more in the height direction (vertical axis) and a resolution of 1 μm or more in the width direction (horizontal axis), with measurement conditions of a measurement length of 100 μm, a sampling interval of 0.54 μm, and a distance of 50 μm between cross-sectional profiles perpendicular to the sliding direction, and the average inclination angle is 1.5° or less.

7. A molded article according to claim 6, which is a fitting component for chemical solutions.

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